Frequency management and SETI: threats to SETI observations in the 1–3 GHz band

The nature of a SETI search makes observations uniquely vulnerable to radio frequency interference because the frequency of a possible ETI signal is unknown. Sensitive radio telescopes, sophisticated software and enhanced signal detection equipment are employed to detect faint signals in the 1–3 GHz frequency range. Frequency management at SETI occurs within a policy environment of the ITU spectrum allocation process. Increased demand by commercial satellite services for access to spectrum adjacent to bandwidth allocated to radio astronomy creates severe international and domestic pressures on SETI observations. Strategies for addressing the RFI problem at the international level will be discussed that include a contingency ITU allocation plan for exclusive use of a particular frequency range by SETI in the event a signal is detected. The lunar farside is, by international agreement, a radio quiet zone for use by radio astronomers. Protected from most human-generated emissions, a SETI radio telescope array on the lunar farside would provide reliable data with minimum interference.     

The SERENDIP SETI project: new instrumentation for SETI and results of recent observations

Over the past 30 years research into the existence of extraterrestrial life has focused on attempts to detect stable narrowband radio signals emitted in the microwave portion of the radio frequency (RF) spectrum. The SERENDIP SETI group is currently conducting search operations on the world’s largest radio telescope at the Arecibo Observatory in Puerto Rico.The third generation SERENDIP system, SERENDIP III, is a 4 million channel FFT-based spectrum analyzer with 0.6 Hz frequency resolution. In this paper, we will discuss the results of our recent 3.5 year sky survey. SERENDIP looked at 95% of the sky visible from Arecibo in the 424–436 MHz range, analyzed 10¹⁴ spectral bins, and logged information on over 2.5×10⁸ signals.The fourth generation SERENDIP system expands on the SERENDIP III design. SERENDIP IV computes 2×10¹¹ operations each second, providing spectral analysis on 160 million channels in 1.7 s. We will discuss the design and use of the SERENDIP IV system and future observing plans.     

Radio frequency interference at Jodrell Bank Observatory within the protected 21 cm band

Radio frequency interference (RFI) will provide one of the most difficult challenges to systematic Searches for Extraterrestrial Intelligence (SETI) at microwave frequencies. The SETI-specific equipment is being optimized for the detection of signals generated by a technology rather than those generated by natural processes in the universe. If this equipment performs as expected, then it will inevitably detect many signals originating from terrestrial technology. If these terrestrial signals are too numerous and/or strong, the equipment will effectively be blinded to the (presumably) weaker extraterrestrial signals being sought. It is very difficult to assess how much of a problem RFI will actually represent to future observations, without employing the equipment and beginning the search. In 1983 a very high resolution spectrometer was placed at the Nuffield Radio Astronomy Laboratories at Jodrell Bank, England. This equipment permitted an investigation of the interference environment at Jodrell Bank, at that epoch, and at frequencies within the 21 cm band. This band was chosen because it has long been "protected" by international agreement; no transmitters should have been operating at those frequencies. The data collected at Jodrell Bank were expected to serve as a "best case" interference scenario and provide the minimum design requirements for SETI equipment that must function in the real and noisy environment. This paper describes the data collection and analysis along with some preliminary conclusions concerning the nature of the interference environment at Jodrell Bank.     

A search of the IRAS database for evidence of Dyson Spheres

One of the forms of astroengineering activity that a very advanced civilization could possibly carry on is the constructions of huge “buildings” in space around the central star. Historically such constructions are called Dyson Spheres. We would like to introduce a new name — Astroengineering Constructions (AC) — to mean a more general type of construction not necessarily related to any specific star. AC absorb energy from different types of activity and re-emit it as infrared radiation, i.e. radiation lying in the submillimeter and millimeter range. Further, AC are expect to have spectra similar to the black-body spectra because they re-emit all the energy that they absorb, although in the infrared range, as already mentioned. Thus, the effective temperature of these Planckian distributions is expected to lie between 3–300 K with the spectrum peaking between 10 μm and 10 mm. We have analyzed the IRAS database and extracted a catalog of sources whose spectra are similar to the black-body emission. The catalog of these sources and their preliminary parameters are discussed. The distribution of the color temperatures of IRAS sources and the sky distribution of sources are also considered. The possibility of the distinction of AC from thick circumstellar dust shells around red giant stars is discussed.     

Recent progress on the lunar farside crater Saha proposal

The aim of this review, whose title might as well be “Toward a dedicated lunar farside radio observatory”, is to provide information for potential interested workers whom we invite to contribute to this multidisciplinary effort.First point: in view of the dramatic increase of radio interference due to the development of satellite-based human telecommunications, it will soon become impossible to conduct valuable high-sensitivity SETI observations from the terrestrial ground. It is why a few years ago I started an interdisciplinary and international endeavor to protect for the next 20/30 years a well specified lunar farside crater (Saha) which no Earth- or geostationary orbit-based radio emission could reach.After raising technical, programmatic, legal, astronautical, industrial, political, ethical issues at a number of conferences of international learned institutions, this enterprise is now of interest for the wider field of next generation high-sensitivity radioastronomy at large, from decametric to sub-millimetric waves.This last year, positive results were the creation of an IAA Sub-committee for “A Lunar SETI Study”, the presentation of a Resolution to the IAU for the protection of a potential lunar radio observatory site, discussions at the IAA/IISL Scientific-Legal Roundtable on SETI & Society at IAF Congress in Torino, the organization of a half-day Scientific Event at next COSPAR Assembly in Nagoya and the initiation of an IAA Cosmic Study on the subject.We shall conclude by outlining the next efforts to be initiated up to a real Moon radio observatory.     

Analysis of a crossed Bragg cell acousto-optical spectrometer for SETI

The search for radio signals from extraterrestrial intelligent beings (SETI) requires the use of large instantaneous bandwidth (500 MHz) and high resolution (20 Hz) spectrometers. Digital systems with a high degree of modularity can be used to provide this capability, and this method has been widely discussed. Another technique for meeting the SETI requirement is to use a crossed Bragg cell spectrometer as described by Psaltis and Casasent. This technique makes use of the Folded Spectrum concept, introduced by Thomas. The Folded Spectrum is a 2-D Fourier Transform of a raster scanned 1-D signal. It is directly related to the long 1-D spectrum of the original signal and is ideally suited for optical signal processing. The folded spectrum technique has received little attention to date, primarily because early systems made use of photographic film which are unsuitable for the real time data analysis and voluminous data requirements of SETI. An analysis of the crossed Bragg cell spectrometer is presented as a method to achieve the spectral processing requirements for SETI. Systematic noise contributions unique to the Bragg cell system will be discussed.     

A search for narrow band signals with SERENDIP II: a progress report

Commensal programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. Our automated commensal system, SERENDIP II, is a high resolution 131,072 channel spectrometer. It searches for 0.49 Hz signals in sequential 64,700 Hz bands of the IF signal from a radio telescope being used for an astronomical observation. Upon detection of a narrow band signal with power above a preset threshold, the frequency, power, time, and telescope direction are recorded for later study. The system has been tested at the Hat Creek Radio Astronomy Observatory 85 ft telescope and the NASA-JPL Deep Space Station (DSS 14) 64 m telescope. It is currently collecting data at the National Radio Astronomy Observatory 300 ft telescope.     

SETI via Wormholes

The special theory of relativity rests on the assumption that in no case can the speed of light be exceeded. Rather surprisingly, however, recent advances in the general theory of relativity show that Faster-Than-Light (FTL) travel is allowed by Einstein’s gravitational theory. An explanation of this apparent contrast between special and general relativity lies in the fact that general relativity uses non-linear differential equations and non-Euclidean spacetime geometry that special relativity does not. Therefore, this larger mathematical armoury makes room for a whole new class of very subtle and unexpected relativistic phenomena to come to light. One of these is the Theory of Wormholes, more politely termed Tunnels into Space–Time. In 1988, Kip S. Thorne and Michael S. Morris published a path-breaking paper about Wormholes showing how spaceflight between two stars might be possible in a time of hours if a “tunnel” dug into space–time exists between them. However, they also showed that keeping the tunnel open for the spaceship to travel through would require a kind of matter, called “exotic” by them, that does not appear to exist in nature, because its tensional strength would have to exceed the energy density of its matter. This request is a severe constraint to the natural existence of Morris–Thorne Wormholes, or even to their artificial construction by an advanced civilization. In 1995, however, the present author sought to replace the exotic matter in a Morris–Thorne Wormhole by a very intense magnetic field. Such “Magnetic Wormholes” could indeed exist because very intense magnetic fields are already known to exist on the surface of neutron stars and pulsars. This paper discusses the consequences on SETI of the possible existence of Magnetic Wormholes. Phenomena of divergent gravitational lensing might possibly occur in the proximity of pulsars and neutron stars. These effects could help us detect signals from very far civilisations by virtue of ordinary SETI techniques already in use.     

Electrostatic Noise Spectrum at the Electron Cyclotron Frequency and Electromagnetic Emission in the Inhomogeneous Plasma of the Topside Ionosphere

Measurements of the wave emission of the topside ionosphere made onboard the APEX satellite using the electric component of the wave field in the 0.1–10 MHz frequency band are presented. At middle latitudes a wave intensity decrease was observed in the broad-band spectrum of the electrostatic noise at the electron cyclotron frequency. It is shown that a break in the spectrum of electrostatic modes at the electron cyclotron frequency (the absence of the plasma eigen-frequencies) may be a cause of the observed effect. The increase of the intensity at the electron cyclotron frequency in the ionospheric trough and at latitudes above the trough region as compared to middle latitudes may be explained by the capture by plasma irregularities of the electromagnetic emission of the auroral electron fluxes.__________Translated from Kosmicheskie Issledovaniya, Vol. 43, No. 3, 2005, pp. 201–208.Original Russian Text Copyright © 2005 by Izhovkina, Prutensky, Pulinets, Kiraga, Klos, Rothkael.     

Efficiency in SETI

While modern SETI experiments are often highly sensitive, reaching detection limits of 10^?25 W/m² Hz in the radio, interstellar distances imply that if extraterrestrial societies are using isotropic or broad-beamed transmitters, the power requirements for their emissions are enormous. Indeed, isotropic transmissions to the entire Galaxy, sufficiently intense to be detectable by our current searches, would consume power comparable to the stellar insolation of an Earth-size planet.In this paper we consider how knowledge can be traded for power, and how, and to what degree, astronomical accuracy can reduce the energy costs of a comprehensive transmission program by putative extraterrestrials. Indeed, an exploration of how far this trade-off might be taken suggests that extraterrestrial transmitting strategies of civilizations only modestly more advanced than our own would be, as are our SETI receiving experiments, inexpensive enough to allow multiple efforts. We explore the consequences this supposition has for our SETI listening experiments.     

Radio wave propagation in the turbulent solar plasma using three satellites

The radio wave propagation in the solar-wind plasma was investigated before and after Mars-2, Mars-7 and Venera-10's superior conjunction. It was found that the moving turbulent solar-wind plasma produced the amplitude and frequency fluctuations and the spectral broadening of monochromatic radio waves. When the Sun-Earth-spacecraft angle decreases from 6° to (0.6) the bandwidth of spectral broadening increases from (0.3) Hz to 300 Hz. The region of 2.5–4° is specific since the bandwidth of spectral broadening is independent of Sun-Earth-spacecraft angle. The spectrum of frequency fluctuations could be represented by a power law with a spectral index of 0.7 ± 0.2. The temporal frequency spectra of the amplitude have two distinct regions. In the low-frequency region the spectral density is approximately constant. The high-frequency portion of the amplitude spectrum follows the power law with a spectral index of 2.8 ± 0.4. The turbulence characteristics of a solar-wind plasma are determined from the experimental data obtained. The three-dimensional wave-number spectrum of irregularities is found to be close to the Kolmogorov-Oboukhov spectrum.The solar-wind density fluctuations decline with heliocentric distance very steeply, but in the distance interval of 7 × 10⁶ – 12 × 10⁶ km, there is a region of enhanced turbulence which could be caused by shock waves.     

SETI and space law: jurisprudential and philosophical considerations for humankind in relation to extraterrestrial life

The impact of confirmation of life outside the small ecosphere we call Earth will be profound on the terran population as a whole. The “Declaration Of Principles Concerning Activities Following The Detection Of Extraterrestrial Intelligence” and the IAA Position Paper “A Decision Process for Examining the Possibility of Sending Communications To Extraterrestrial Civilizations: A Proposal” provide a firm basis for the development of a new body of space law. It is important that space law design and prepare for implementation of a protocol to guide the nations of the world concerning the search for extraterrestrial intelligence (SETI), through the advice and cooperation of scientists, jurisprudential, philosophical, political and sociological scholars. Through the IAA, the IISL, the United Nations and other organizations, formal documentation should be drafted to encode the Declaration of Principles and IAA Position Paper referred to above. In this way, a body of metalaw can be developed to enable human communication with non-terrestrial life. This paper discusses the philosophical and sociological parameters of terran understanding of our place in the universe which will dramatically impact jurisprudential thought and action in light of the realization of the infinitesimally small niche that humankind occupies. A discussion of these interdisciplinary concerns will be necessary to realize a metalegal approach to interstellar communications and relations.     

非参数化迭代自适应SAR射频干扰抑制方法

合成孔径雷达（Synthetic Aperture Radar，SAR）的成像质量与图像解译精度会因为空间中存在的射频干扰（Radio Frequency Interference，RFI）而下降。本文在加权最小二乘迭代自适应算法的基础上，提出了非参数化的迭代自适应RFI抑制方法。该方法在成像处理前增加了对RFI的预检测环节，在初步检测出存在RFI的数据部分后只对存在RFI的数据进行SG（Savitsky-Golay，萨维茨基·戈莱）卷积平滑处理以提升对弱RFI的检测能力。利用带阻滤波器滤除存在干扰的频段后，使用迭代自适应处理在频谱中估计出被去除频段中的信号分量以获得期望的距离谱。与利用传统距离频率滤波方法进行RFI抑制相比，所提出的方法在图像细节保持方面效果更优，避免了因频谱不连续而导致的旁瓣增加，且运算效率更高。     

Positive consequences of SETI before detection

Even before a signal is detected, six positive consequences will result from the scientific search for extraterrestrial intelligence, usually called SETI. (1) Humanity’s self-image: SETI has enlarged our view of ourselves and enhanced our sense of meaning. Increasingly, we feel a kinship with the civilizations whose signals we are trying to detect. (2) A fresh perspective: SETI forces us to think about how extraterrestrials might perceive us. This gives us a fresh perspective on our society’s values, priorities, laws and foibles. (3) Questions: SETI is stimulating thought and discussion about several fundamental questions. (4) Education: some broad-gage educational programs have already been centered around SETI. (5) Tangible spin-offs: in addition to providing jobs for some people, SETI provides various spin-offs, such as search methods, computer software, data, and international scientific cooperation. (6) Future scenarios: SETI will increasingly stimulate us to think carefully about possible detection scenarios and their consequences, about our reply, and generally about the role of extraterrestrial communication in our long-term future. Such thinking leads, in turn, to fresh perspectives on the SETI enterprise itself.     

Measurement of Vibration Microaccelerations onboard the Mir Orbital Station Using the VM-09 System of Accelerometers

The results of processing the data of measurements of microaccelerations, carried out onboard the Mir orbital station using the Russian VM-09 system of accelerometers, are described. The system was developed by the Composite Research-Production Association. The sensitivity of this system was 10^–4 m/s²; its frequency band had limits from a few tenths of a hertz up to 100 Hz. The measurements were carried out in the real-time mode of data transmission to the Earth, when the orbital station flew over the telemetry data receiving point. The instrument's sampling rate was 200 measurements per second, and the length of a continuous run of measurements did not exceed 10 min. The following problems are considered in the paper: (1) isolation of cyclic trends from the measurement data; (2) estimation of spectral density of the data component with a continuous spectrum; and (3) low-frequency filtration of the measurement data     

A new 6 MHz 128.000 channel spectrum analyzer

We present an FFT-based digital spectrometer designed for SETI and Radioastronomy applications. In the typical configuration, the system is capable of supplying the spectrum of the received signal every 28.8 ms, for a maximum 128 K (131,072) frequency bins at an input bandwidth of 6 MHz.     

Results of Measurements of Accelerations of Technological Devices onboard the FotonSpacecraft

This paper generalizes the results of measuring the residual accelerations arising when investigations in space materials science are carried out onboard the unmanned Fotonspacecraft. The levels of vibroaccelerations are analyzed in the frequency band of 1–500 Hz for the technological devices UZ01, UZ04, and POLIZON, developed by the Federal Unitary State Enterprise Barmin Design Bureau of General Machine Building (V.P. Barmin KBOM). The levels of accelerations are estimated in the frequency band of 0–1 Hz in the zone of technological operations of these facilities. The basic sources of vibroaccelerations acting upon the frames of devices are determined in the capsule zone, where technological processes of producing new materials take place. In the frequency band of 1–500 Hz the vibroaccelerations are shown to be generated by the operation of Fotonspacecraft units and a drive of capsule translation during the technological process. On the capsule frame they reach the values of (1–3) × 10^–3 g. The level of linear accelerations in the infralow-frequency band is determined by rotational motions of the Fotonspacecraft. It depends on the device location with respect to the spacecraft center of mass and does not exceed (1–7) × 10^–6 gin the steady-state regime in the zone of technological activity.     

Hesperides: Solar/nuclear missions to the Sun׳s inner gravity focus

The Sun?s gravity focus at >550 AU is of interest to astrophysicists including SETI scientists, researchers seeking to image extra-solar planets and others. One method for an extra-solar probe to reach the Sun?s inner gravity focus within a human working lifetime (less than 50 years) is to combine solar and nuclear propulsion techniques. Here, we present a non-optimized probe concept including state-of-the-art solar-sail, radioisotope-electric propulsion and giant-planet gravity assists. Application of radioisotope propulsion allows some cross range capability during and after the powered and cruise phases of the flight to >600 AU. Such a capability is likely necessary to fully utilize the solar gravitational lens effect for SETI and astrophysical observations.     

Autonomic function testing aboard the ISS using “PNEUMOCARD”

Investigations of blood pressure, heart rate (HR), and heart rate variability (HRV) during long term space flights on board the “ISS” have shown characteristic changes of autonomic cardiovascular control. Therefore, alterations of the autonomic nervous system occurring during spaceflight may be responsible for in- and post-flight disturbances. The device “Pneumocard” was developed to further investigate autonomic cardiovascular and respiratory function aboard the ISS. The hard-software diagnostic complex “Pneumocard” was used during in-flight experiment aboard ISS for autonomic function testing. ECG, photoplethysmography, respiration, transthoracic bioimpedance and seismocardiography were assessed in one male cosmonaut (flight lengths six month). Recordings were made prior to the flight, late during flight, and post-flight during spontaneous respiration and controlled respiration at different rates.HR remained stable during flight. The values were comparable to supine measurements on earth. Respiratory frequency and blood pressure decreased during flight. Post flight HR and BP values increased compared to in-flight data exceeding pre-flight values. Cardiac time intervals did not change dramatically during flight. Pulse wave transit time decreased during flight. The maximum of the first time derivative of the impedance cardiogram, which is highly correlated with stroke volume was not reduced in-flight.Our results demonstrate that autonomic function testing aboard the ISS using “Pneumocard” is feasible and generates data of good quality. Despite the decrease in BP, pulse wave transit time was found reduced in space as shown earlier. However, cardiac output did not decrease profoundly in the investigated cosmonaut.Autonomic testing during space flight detects individual changes in cardiovascular control and may add important information to standard medical control. The recent plans to support a flight to Mars, makes these kinds of observations all the more relevant and compelling.